In a photolithography process in manufacture of a semiconductor device, for example, various kinds of heat processing such as heat processing of causing a solvent in a resist film applied on a wafer to evaporate (pre-baking), heat processing of accelerating the chemical reaction in the resist film after exposure of a pattern (post-baking), heat processing after developing treatment (post-baking) and so on are performed.
The above-described heat processing is usually performed in a heat processing apparatus including a circular heating plate by mounting the wafer on the heating plate which has been set to a predetermined temperature. However, for example, when there is extraneous matter such as debris on the heating plate, the wafer to be mounted on the heating plate is placed over the extraneous matter, with the result that the wafer will not be uniformly heated within the wafer. If the wafer is not uniformly heated, for example, the line width of the pattern to be formed on the wafer finally varies within the wafer, resulting in decreased yields. For this reason, if extraneous matter adheres on the heating plate, the matter needs to be detected.
When the wafer is mounted on the heating plate in heat processing, the heat of the heating plate is drawn by the wafer, so that the temperature of the heating plate temporarily drops. For this reason, if the wafer is not appropriately mounted on the heating plate because of adherence of the extraneous matter on the heating plate, less heat transfers from the heating plate to the wafer than that in the case where the wafer is normally mounted, resulting in a smaller temperature fluctuation of the heating plate. Conventionally, this phenomenon is utilized to calculate the integrated value of temperature fluctuation of the heating plate when mounting the wafer on the heating plate, and compare the integrated value to a previously set threshold value, whereby the extraneous matter on the heating plate can be detected (Patent Document 1).
[Patent Document 1]
Japanese patent Application Laid-open No. 2002-50557